This thesis describes the synthesis and characterisation of new examples of meso-n1-organometallic porphyrins. These porphyrins were originally encountered as catalytic intermediates in the C-C bond forming reaction on the porphyrin periphery using palladium catalysts. They have now become a research topic in their own right and no other examples of this type of organometallic porphyrins had been reported at the outset of this work. In Chapter 2, several examples of meso-palladioporphyrins were prepared in high yield using oxidative addition of the porphyrin-bromine bond to a suitable Pd(0)phosphine precursor. These phosphine precursors were prepared from Pd(PPh3)4 or Pd2dba3 plus either PPh3 or a chelating diphosphine. Several new examples of mono- and di palladium complexes of chelating diphosphines were prepared. Chapter 3 looks at the preparation of meso-platinioporpyrins and the insertion of various central metal ions into the porphyrin ligand. Pairs of cis- and transisomers of the Pt(II) complexes were isolated from the oxidative addition of Pt(PPh3)3 to the free base and Ni(II) bromoporphyrins. The cis-isomer converted to the trans upon heating. At room temperature the two isomers are geometrically stable and survive unchanged through column chromatography and slow recrystallisation. The central metal ion can be introduced either before or after the oxidative addition to Pt(0). However, it is preferable to insert the metal ion last as the complexes of Br(MDPP) are rather insoluble (especially that of MnCl) and are more difficult to handle than the common intermediate trans- [PtBr(H2DPP)(PPh3)2]. The oxidative addition of Pt(dba)2 to meso-bromo-DPP in the presence of PPh3 has also been shown to be an effective method of synthesising n1-organo platinum porphyrins in high yield. However, this method was unsuccessful when using chelating diphosphines. In Chapter 4, the physical properties of meso- metalloporphyrins are reported including electrochemistry, fluorescence spectroscopy and crystal structure determinations. The fluorescence intensities of the meso-substituted porphyrins (freebase and zinc complexes) are dramatically reduced in comparison with the unsubstituted porphyrins. This fluorescence quenching is a dramatic example of the "heavy atom effect". Electrochemical measurements of freebase and Ni(II)porphyrins indicate that the organometallic fragment is a strong electron donor. The visible absorption spectra for all Pd(II) and Pt(II) complexes are typical for diarylporphyrins. All groups other than H in the 5- or 5- and 15-positions cause a red shift of the major absorption bands for both the free bases and central-metal complexes. The crystal structure studies of the Pt(II) complexes include the complexes, cis- [PtBr(MDPP)(PPh3)2] (M = H2, Ni), trans-[PtBr(MDPP)(PPh3)2] (M = H2, Ni, Zn and Co), trans-[PtCl(H2DPP)(PPh3)2] and trans-[PtBr(NiDPPBr)(PPh3)2]. In all these structures, the free bases are virtually planar while the metallo derivatives adopt a hybrid of the ruffled and saddled conformations. Chapter 5 contains the initial studies of chiral palladioporphyrins, using three different types of chiral chelating diphosphine ligands. These chiral palladioporphyrins are readily prepared by oxidative addition of the Pd(0) precursor with bromoporphyrin. The asymmetry of the chiral ligand is detectable at the remote B-pyrrole protons in all the chiral complexes as eight doublets are observed in 1H NMR spectra. The chirality of these ligands in the porphyrin complexes induces circular dichroism in the region of the porphyrin electronic absorption. High optical activity is observed for the BINAP complexes.